Multiple nanosecond laser pulse anneal processes and resultant semiconductor structure

ABSTRACT

Semiconductor structures and methods of fabricating the same using multiple nanosecond pulsed laser anneals are provided. The method includes exposing a gate stack formed on a semiconducting material to multiple nanosecond laser pulses at a peak temperature below a melting point of the semiconducting material.

FIELD OF THE INVENTION

The invention relates to semiconductor structures and, moreparticularly, to semiconductor structures and methods of fabricating thesame using multiple nanosecond pulsed laser anneals.

BACKGROUND

In increasing performance of a FET, it is known that gate dielectricreliability vs. Tiny scaling is a major industry trade-off. For example,increasing the thickness of a dielectric material stack increasesreliability of the semiconductor device, but this increase in stackthickness will also decrease performance. Conversely, decreasing thethickness of a dielectric material stack can decrease reliability of thesemiconductor device, but this decrease in stack thickness will alsoincrease performance.

Also, as MOSFET devices are scaled down to less than 100 nanometers ingate or channel length, highly doped, shallow source and drain extensionregions can be employed to achieve high drive current capability. Thedopants are activated by conducting laser annealing or othermillisecond-scale (mSec) annealing of the implanted extension regionseither prior, during, or after a more conventional, second-scale RapidThermal Anneal (RTA).

Laser annealing can be characterized by the duration of exposure to itsradiation. Pulsed lasers, for example, operate in a nanosecond-rangeregime with exposure durations of tens to two hundreds of nanosecondswith a typical exposure time of less than one hundred nanoseconds. Atsuch short anneals, thermal activation of dopants can be inefficient.Consequently, the dopant activation process relies on a phase transitionsuch as melting-recrystallization of amorphized and dopedsemiconductors. Due to this reason, nanosecond-scale laser annealing isalso referred to as melt laser annealing or pulsed laser annealing.Nanosecond-scale laser annealing also has a very large temperaturepattern effect because the laser energy absorbed in surfacemicrostructures does not have sufficient time to spread uniformly withinthe substrate via thermal diffusion. In addition to large patterneffects, its reliance on inducing phase transitions in microstructuresproduces substantially different levels of dopant activation nearexposure edges or in areas of exposure overlap.

In contrast, millisecond-scale “mSec” laser annealing has exposure timesranging from tens of microseconds to tens of milliseconds. In thisrange, thermal activation of dopants can be efficient, and theconcentration of active dopants is generally proportional to the peakanneal temperature. Continuous wave lasers are employed in this regime.Since the laser beam is shaped in the form of a line, the wafer surfaceis raster scanned, which means that it is scanned as a pattern ofparallel lines or curves. In this case, the exposure time (also referredto as the dwell time) is equal to the characteristic beam width in thescanning direction (often defined at full width at half maximum (FWHM))divided by the scan speed. The beam length (e.g., about 10 millimeters(mm)) perpendicular to the scanning direction (often defined at fullwidth at 95-99% of the maximum) is usually much smaller than the wafersize (e.g., about 300 mm). As such, adjacent scans (also referred to asexposures) are often applied with some overlap to completely cover theentire wafer surface. In the overlap region, the wafer surface isexposed and annealed twice.

SUMMARY

In an aspect of the invention, a method comprises exposing a gate stackformed on a semiconducting material to multiple nanosecond laser pulsesat a peak temperature below a melting point of the semiconductingmaterial.

In an aspect of the invention, a method comprises forming a transistoron a semiconducting material. The transistor comprises a gate stackcomposed of high-k dielectric material and gate material. The methodfurther comprises exposing the gate stack to multiple nanosecond laserpulses at a peak temperature below a melting point of the semiconductingmaterial, post gate dielectric deposition.

In an aspect of the invention, a method comprises forming a transistoron a semiconducting material. The transistor comprises a gate stackcomposed of high-k dielectric material. The method further comprisesexposing the gate stack to 10×40 nanosecond pulses at a peak temperaturewhich is below a melting point of the semiconducting material, post gatedielectric deposition.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIG. 1 shows a representative transistor (FET) in accordance withaspects of the invention.

FIG. 2 shows a representative temperature-time trace of the nSec laseranneal process in accordance with the present invention.

FIG. 3 shows a reliability graph of NBTI using pFET cells shown in TABLE1.

FIG. 4 shows another reliability graph of NBTI using the pFET cellsshown in TABLE 1.

FIG. 5 shows a comparison graph of threshold voltage, Vt, using the pFETcells shown in TABLE 1.

FIG. 6 shows a comparison graph of mobility using the pFET cells shownin TABLE 1.

DETAILED DESCRIPTION

The invention relates to semiconductor structures and, moreparticularly, to semiconductor structures and methods of fabricating thesame using multiple nanosecond pulsed laser anneals. More specifically,the processes described herein provide significant improvement ofnegative-bias temperature instability (NBTI) in a semiconductorstructure using multiple nanosecond pulsed laser anneals of a high-kstack of a gate structure.

In embodiments, the nanosecond pulsed laser anneals described hereincomprises multiple laser pulses in the nanosecond range, of a high-kmaterial or stack of materials including a high-k material, at peaktemperatures below the melting point of the semiconducting material. Inmore specific embodiments, the multiple nanosecond pulsed laser annealshave a peak temperature below the melting point of the semiconductingmaterial in the range from about 800° C. to about 1400° C., with a laserpulse duration of 10-100 nSec, ranging from 2 to 100 pulses and morepreferably 5 to 100 pulses, for example. In embodiments, the cumulativelaser exposure time preferably ranges from 300 nanoseconds to 3microseconds. In embodiments, the multiple nanosecond pulsed laseranneals can be performed post gate deposition due to the peaktemperature being below the melting point of both semiconducting andgate materials.

Advantageously and unexpectedly, the inventors observed that byperforming the multiple pulsed laser anneals described herein it ispossible to achieve a significant improvement in NBTI on the order ofapproximately 200 mV of maximum gate voltage using Voltage-Ramp-Stress(VRS) NBTI measurement method. In embodiments, the superior improvementin NBTI, e.g., approximately 200 mV of maximum gate voltage, wasachieved using, e.g., a 10× nSec anneal; although other parameters asdescribed herein will also achieve these superior and unexpectedresults. It was also unexpectedly found by the inventors that NBTIimprovement scales with the number of nSec laser anneal pulses orcumulative nSec laser exposure time; something that is counterintuitiveand unexpected taking into consideration that a single submelt nSecanneal should technically have no significant, if any, effect ondielectric material properties, e.g., crystallinity and thickness of thedielectric. In further embodiments, no significant changes in nFETparameters including positive bias temperature instability (PBTI),mobility and equivalent oxide thickness were exhibited using themultiple pulsed laser anneals described herein.

Performance of a semiconductor device typically has an inverserelationship to reliability. There are several ways to affectperformance and reliability of a semiconductor device. For example,increasing the thickness of a dielectric material stack increasesreliability of the semiconductor device, but this increase in stackthickness will also decrease performance. Conversely, decreasing thethickness of a dielectric material stack can decrease reliability of thesemiconductor device, but this decrease in stack thickness will alsoincrease performance.

Additionally, performance can be increased using different dielectricmaterials such as high-k dielectrics or different gate stack metals ormaterials. The effect of introducing high-k dielectrics is equivalent tothinning down gate dielectric equivalent “electrical” thickness at itsgiven physical thickness. But, different dielectric materials willresult in different magnitudes of their internal electric fields under aconstant external bias that will lead to different values of theirtime-dependent dielectric breakdown (TDDB), which is a failure mechanismin FETs when the gate oxide breaks down as a result of long-timeapplication of relatively low electric field. The breakdown is caused byformation of a conducting path through the gate oxide to substrate dueto a slow degradation of its insulating property, when FETs are operatedclose to or beyond their specified operating voltages. Althoughultrathin dielectric stacks typically have greater performanceparameters, they also typically undergo a catastrophic breakdowncompared to thicker dielectric stacks, thus affecting overallreliability.

While TDDB is an example of catastrophic failure, bias temperatureinstabilities (BTIs) of transistor gates are examples of continuousdegradation in transistor performance during its normal operation.During normal product operation, an nFET gate is biased positively withrespect to its body causing positive BTI or PBTI, while a pFET gate isbiased negatively causing negative BTI or NBTI. Both BTIs are caused bya slow modification of gate dielectric material properties while underelectrical bias. Modified gate dielectric properties affect transistorthreshold voltage and, consequently, its performance. While the speed ofBTI degradation has a typical inverse relationship to the gatedielectric thickness, it is also affected by the choice of gatematerials and fabrication processes. As should be understood by those ofskill in the art, BTI's are dielectric material properties which relateto the quality of interfaces and bulk dielectric materials. Accordingly,NBTI and PBTI metrics adjusted for the gate dielectric thickness can beviewed as material properties of respective pFET and nFET gate stacksquantifying their resistance to modifications under electrical bias.

There are several test methods to assess the speed of BTI degradation.These test methods lead to different metrics that will be brieflydiscussed here. One such test method is referred to as a ConstantVoltage Stress (CVS) test and another method is known as a Voltage RampStress (VRS) test. BTI tests are conducted at an elevated temperature of125° C. to speed up degradation effects. In the CVS method, a constantvoltage Vg is applied on the gate terminal of a transistor for durationthat increases on a logarithmic scale. The corresponding Vt shift, □Vt,is measured as a function of stress time. The result is written in termsof time (relates to the transistor lifespan) during which the thresholdvoltage shifts by a certain preset value. In this form, the result isgreatly affected by the chosen stress gate voltage. A higher gatevoltage results in shorter transistor lifespan. CVS test is typicallyconducted at an elevated gate bias to shorten the stress time and thenprojected to the transistor operating voltage using statistical methodsof accelerated testing. In contrast, in the VRS method, a ramped stressvoltage with a certain ramp rate is applied to the gate terminal and thethreshold voltage is assessed continuously during the test. As the gatevoltage ramps, the threshold voltage shift is measured. The result ofthis test is generally written in terms of maximum gate voltage (relatesto the maximum operating voltage) at which the threshold voltage shiftsby a certain preset value, typically, 50 mV. The higher the gatevoltage, Vg, for the set threshold voltage shift, □Vt, of 50 mV, themore reliable the gate stack in terms of respective BTI's. Underassumptions of accelerated testing, both the VRS and CVS test methodsare shown to be equivalent but converting different BTI reliabilitymetrics requires the use of sophisticated accelerated testing models.

Different process conditions can also affect performance and reliabilityof the semiconductor device since they affect material properties of thedielectric gate stacks. The dielectric layers are initially formed ordeposited as an amorphous laminate. Various chemical and thermalpost-treatments are applied to reduce dielectric stack equivalentelectrical thickness and to improve the quality of materials. Inaddition, the gate stack may be subjected to additional thermalpost-treatments that are directed to enabling other process modules suchas dopant activation, stress engineering, silicidation, interconnects,and others. Thermal post-treatments are characterized by their durationand ramp up/down rates. A number of investigators and practitionersassessed the effect of shortening thermal post-treatments fromsecond-scale, slow cool down (<100° C./sec) Rapid Thermal Annealing orSpike Annealing to millisecond-scale, fast quench (>1e5° C./sec) LaserAnnealing or Laser Spike Annealing onto NBTI reliability and found thatthe application of millisecond laser annealing degrades NBTI reliabilityand requires a method for its recovery. See, e.g., Cho et al.,Interface/Bulk Trap Recovery After Submelt Laser Anneal and the Impactto NBTI Reliability. It has been observed that an application ofmillisecond-scale laser spike annealing will result in creating bulk andinterfacial traps within SiOx/HfSiO/AlO/TiN high-k, metal gate pMOSstack and degraded NBTI reliability. It has been further observed thatan application of longer, second-scale RTA after the millisecond annealpartially heals generated traps and recovers NBTI reliability. It hasbeen suggested that a longer RTA post-treatment allows enough time forhealing dielectric defects generated during high-temperature laserannealing and preserved by its fast cool down rate or quenching. See,e.g., Chen et al., A Novel Method to Improve Laser Anneal WorsenedNegative Bias Temperature Instability in 40-nm CMOS Technology, IEEETransactions on Electron Devices, Vol. 38, No. 3, March 2011. Similar toCho et al., it has been shown that the application of millisecond-scalelaser or flash-lamp annealing results in a degraded NBTI of SiON/PolySipMOS gate stack. It has been further observed that an application of asecond-scale RTA after the millisecond anneal partially recovers NBTIreliability. Moreover, in F. Wan Muhamad Hatta et al., LaserAnneal-Induced Effects on the NBTI Degradation of Advanced-Process 45 nmhigh-k PMOS, Advanced Materials Research Vols. 189-193 (2011) pp1862-1866, NBTI reliability degradation was observed subsequent to theintegration of millisecond-scale laser annealing (LA) in the processflow of a SiOx/HfO₂/TiN gate stack PMOS device. Clearly, short-duration,high-temperature anneals with a fast cool down or quenching are foundand believed to be detrimental to NBTI reliability irrespective ofspecific dielectric layers employed within pMOS gate stacks.

Thermal post-treatments of high-k dielectric stacks may also inducecrystallization of amorphous high-k layers. The crystallizationthreshold temperature depends on specific high-k materials used in thestack and is about 800-850° C. for the ultrathin (<3 nm) hafnium oxidelayers and is about 400-500° C. for similar zirconium oxide layers, forinstance. The size of crystallites also depends on speed and duration ofcrystallizing anneals: generally, smaller crystallites are produced byshorter, faster anneals. Consequently, the observable crystallizationtemperature for millisecond anneals is about 200-300° C. higher than thecrystallization threshold temperature measured using isothermalannealing with long durations. Typical size of crystallites produced bymillisecond-scale anneals is found to be around 1.5-2 nm with a mixtureof monoclinic and tetragonal phases co-existing within ultrathin HfO₂films. In order to distinguish between different crystallizationthreshold temperatures and resultant crystallite sizes, thecrystallization induced by millisecond anneals will be referred to asmicro-crystallization. Crystallizing anneals are known to improve BTIreliability parameters of the stacks when compared to anneals whichpreserve amorphous layers. However, crystallization of high-k layersalso results in multiple detrimental side effects. Crystallizationreleases excess oxygen atoms from the high-k film causing growth orthickening of the low-k interfacial layer. Further, the crystallinehigh-k material has a higher speed of diffusion for oxygen atoms andoxygen vacancies allowing for their transport from transistor exteriorto its channel region where they affects threshold voltage anduniformity of the interfacial layer. Crystallization of high-k materialmay also retard the diffusion of useful additive metallic atoms such Laor Mg that are often employed for producing multiple threshold voltagetransistors. This, in turn, suppresses the freedom of adjustingthreshold voltage of select transistors. In addition, crystallization ofhigh-k material causes surface roughness and material property variationbetween crystalline grains, which, in turn, results in non-uniformelectrical fields in the channel region adjacent the dielectric film.This, in turn, significantly degrades device performance. In general,the crystallization of high-k films in gate stacks is either avoidedaltogether or postponed until later in the process sequence when high-klayers are sealed mitigating detrimental effects caused byre-crystallization.

Nanosecond (nSec) laser anneal (e.g., 10's to 100 nSec temperaturepulses) has been employed to locally melt materials (e.g., Si, SiGe, Ge,silicides, metal interconnects) to enable forming metastable alloys byquenching the molten phase. To melt materials, the nSec laser pulseanneal is performed above the melting point of the selected material,e.g. an underlying semiconductor. Although a duration of nSec treatmentis known to prevent any collective motion of atoms in the solid state(e.g., no dislocation formation, no re-crystallization, no grain growth,etc.), nonetheless it has been found that submelt nSec laser anneal mayinduce random motion of atoms in the solid phase such as creation ofpoint defects and modifying nearest-neighbor bonding arrangements. Asuper fast cool down rate in excess of 1e8° C./sec freezes any changesinduced by nSec melt or sub-melt laser annealing. Accordingly, it hasbeen believed that a transition to a molten high-k phase would berequired in order to induce high-k layer re-crystallization possiblypositively affecting BTI parameters. Attaining melting point of hafniumoxide high-k material of about 2750° C. would not be of any practicalinterest due to simultaneous melting and/or evaporating underlyingsemiconducting materials with much lower melting points, e.g. meltingsilicon with its melting point of 1410° C. Further, the fast cool downrate or quenching would suggest a possible negative impact on BTIreliability parameters and, more specifically, onto NBTI reliabilityparameters. Clearly based on the above observed properties using ananosecond pulsed anneal process, it would not have been expected thatsignificant improvement in NBTI would occur with any number ofnanosecond anneal pulses, but the fact that the processes of the presentinvention as described herein did possess such significant propertyimprovement was an unexpected result to the inventors.

FIG. 1 shows representative transistor elements in accordance withaspects of the invention. As shown in this representative figure, thestructure 10 includes principle elements of a transistor formed on asemiconductor material 14. The semiconductor material 14 can be composedof any suitable material including, but not limited to, Si, SiGe, SiGeC,SiC, Ge alloys, GaAs, InAs, InP, and other III/V or II/VI compoundsemiconductors. The semiconductor material 14 is lightly doped havingdoping polarity opposite to the FET type, e.g. a lightly doped n-typesemiconducting material for pFET. The structure 10 includes a gate stack12 formed on the semiconductor material 14, and includes a high-kdielectric stack 11 composed of one or more layers of interfacialdielectric 15 and one or more layers of high-k dielectric material 16including, for example, hafnium oxide materials. In embodiments, theinterfacial dielectric can be SiO₂ or SiO_(x)N_(y), as examples. Thegate stack 12 can further include conductive gate material 18 formed onthe high-k dielectric stack 11. In embodiments, the gate material 18 caninclude, e.g., doped polycrystalline semiconducting material ordifferent layers of metallic materials depending on the desired workfunction and performance parameters. The gate stack 12 can furtherinclude sidewall isolation structures 19, e.g., nitride based dielectricmaterial. The transistor structure 10 can further include doped sourceand drain structures and metallic contacts that are not shown. Thesource and drain structures are doped oppositely to the transistor body14, e.g. p-type doped for the n-type pFET body. While the semiconductormaterial 14 is drawn as a horizontal slab, the structure 10 is equallyrepresentative of various three-dimensional transistors where thematerial 14 may be oriented differently and/or may have a differentshape. Such three-dimensional, non-planar transistors include finFETs,surround-gate FETs, multiple-gate FETs, nano-wire or nano-sheet FETs,vertical FETs, and others.

The structure 10 shown in FIG. 1 can be manufactured in a number of waysusing a number of different tools. In general, though, the methodologiesand tools are used to form structures with dimensions in the micrometerand nanometer scale. The methodologies, i.e., technologies, employed tomanufacture the structure 10 have been adopted from integrated circuit(IC) technology. For example, the structures of the present inventionare built on wafers and are realized in films of material patterned byphotolithographic processes on the top of a wafer. In particular, thefabrication of the structure 10 uses three basic building blocks: (i)deposition of thin films of material on a substrate, (ii) applying apatterned mask on top of the films by photolithographic imaging, and(iii) etching the films selectively to the mask. In addition to thesebasic steps, chemical mechanical polishing, ion implantation, andannealing processing steps can be employed. Various elements ofstructure 10 can also be formed using different sequential order. Forinstance, the gate stack 12 can be formed first followed by the spacers19, or alternatively, the spacers 19 can be formed first followed bygate stack 12. The latter approach is known as the replacement gatesequence while the former is known as the gate first sequence.

In accordance with aspects of the present invention, the gate dielectricstack 11 of structure 10 also undergoes a nanosecond laser annealprocess as represented by the arrows in FIG. 1, which significantlyimproves NBTI reliability of pFET gate stack. FIG. 2 shows arepresentative temperature-time trace 30 of the nSec laser annealprocess in accordance with the present invention. Temperature-relatedfeatures of the trace 30 include the substrate preheat level 43,millisecond preheat level 45, level 47 at which millisecond preheatduration is measured, and peak nanosecond level 49. The level 47 istypically referenced to level 45, e.g. 100° C. below it.Duration-related features of the trace 30 include millisecond preheatcharacteristics: duration 50, heat up rate 51, cool and down rate 53;and multiple nanosecond temperature pulses 55. The nanosecondtemperature pulses 55 are characterized by the number of pulses andindividual pulse duration, heat up and cool down rates. While theduration of an individual temperature pulse is directly related to thenanosecond exposure time, they are not equal. The temperature pulse istypically measured at about 100° C. below the peak temperature and isabout 2-4 times shorter than the exposure time that is measured at fullwidth at half maximum (FWHM) of incident laser power density. Thespecifications are often made easier in terms of exposure time ratherthan temperature pulse durations since the exposure time is directlycontrolled during processing. The nanosecond annealing portion oftemperature trace can be also characterized by the cumulative nanosecondexposure time defined as the sum of individual nanosecond pulse exposuredurations. FIG. 2 also shows two temperature limits: crystallizationlimit 35 and melt limit 33. These limits depend on the choice ofsemiconductor material 14 and high-k material 16 and nSec laser annealposition in processing flow sequence.

In accordance with the present invention, the nSec laser anneal can beconducted at various steps after forming dielectric stack 11 but priorto any high-k crystallizing anneals. In some embodiments, the nSecanneal is performed immediately after forming stack 11. In this case,the melt limit 33 is defined by the melting point of semiconductormaterial 14. If material 14 is a compound semiconductor material such asSiGe or III-V compounds, then the melting point for limit 33 is given bythe liquidus temperature of material 14. The crystallization limit 35 isgiven by the micro-crystallization threshold of high-k material 16. Apreferred range for peak temperature of nSec laser anneal (level 49) isfrom above the micro-crystallization limit 35 and below the melt limit33 while a more preferred range is from about 200° C. below the meltlimit 33 to about 50° C. below the melt limit 33. While themillisecond-scale preheat is not required, it is highly preferred due toreduced requirements on nSec temperature swing, needed nSec laser powerdensity, and associated reduction of nSec pattern effects. Accordingly,higher millisecond preheat temperature is desired but it can induceunwanted high-k micro-crystallization. Hence, the preferred range forthe millisecond preheat temperature (level 45) is from about 300° C.below the micro-crystallization limit 35 to about 50° C. below themicro-crystallization limit 35. The preferred duration 50 of millisecondpreheat is from about 0.1 msec to about 5 msec. Preferred range of heatup 51 and cool down 53 rates is from about 1e4 to about 1e6° C./sec.Typical substrate base temperature (level 43) is from the roomtemperature to about 500° C. with 150° C. to 300° C. being preferred. Inalternative embodiments, the nSec laser anneal is performed after someor all elements of conductive structure 18 are formed but prior to anyhigh-k crystallizing anneals. In this case, the melt limit 33 is thelower of melting points of semiconducting material 14 and conductivematerials of structure 18. Typical metallic/conductive elements ofstructure 18 include refractory metals, metal nitrides and carbides suchas W, Co, Ti, Ta, TiN, TaN, TiC, and TaC, all of which have meltingpoints substantially higher than the semiconducting material 14 and,hence, do not affect the melt threshold 33 and the preferred range ofpeak nSec laser anneal temperature 49. More importantly, presence ofconductive elements of structure 18 may put a lower limit ontomillisecond preheat temperature 45 due to a damage to the metal gate athigh-temperature for millisecond duration. In this case, the millisecondpreheat temperature is kept preferably below 800° C. and more preferablybelow 700° C.

In view of the many studies performed, as noted above, it was unexpectedto the inventors that multiple nanosecond laser anneal temperaturepulses would result in significant improvement in NBTI, e.g., on theorder of 200 mV for “Voltage-to-50 mV” metric of VRS test, particularlyin view of Cho, et al., Chen, et al., and Hatta et al. For example, dueto the ultra short pulses, it was expected that either no change or adegradation of reliability parameters would occur when performingmultiple nanosecond pulsed laser anneals in accordance with the presentinvention, e.g., nanosecond anneals with peak temperature below themelting point of both semiconducting and high-k materials; instead, suchprocesses provided a significant improvement in NBTI reliability. Also,due to the ultra short anneal duration of the pulsed nanosecond anneal,the dielectric material of the semiconductor device does not exhibit anymicro-crystallization, nor is there any re-crystallization of othermaterials due to the peak temperature of the anneal being below therespective melting points of these other materials.

More specifically, TABLE 1 shows pFET cells which were subjected todifferent anneal process sequences, post dielectric stack deposition. Inthis case, the semiconducting material was silicon with the meltingpoint of 1412° C., e.g., about 1400° C. Interfacial layer, “IL”, was athin (<1 nm) SiON layer and high-k layer was a ˜2 nm-thick HfO₂. TheHfO₂ crystallization threshold was about 850° C. while amicro-crystallization threshold was about 1050° C.-1100° C. As shown inTABLE 1, pFET wafers in Group I cells were subjected to amicro-crystallizing millisecond anneal at ˜1200° C. peak temperature and˜0.5 msec duration at 1100° C.; whereas, pFET wafers in Group II and IIIwere subjected to a single (1×) nanosecond laser pulse anneal processwith varying nanosecond peak and millisecond preheat temperatures. pFETwafers in Group IV, on the other hand, were subjected to multiple (10×)nanosecond (e.g., ˜40 nanoseconds exposure time) pulsed laser anneals ata peak temperature of ˜1300° C., in accordance with aspects of theinvention. Accordingly, the cumulative nanosecond exposure time for theGroup IV was about 400 nanoseconds and about 40 nanoseconds for groupsII and III. All cells also had an additional RTA anneal at about 1000°C. peak conducted during deposition of conductive gate 18.

TABLE 1 mSec nSec anneal, anneal, Additional Anneal Level 45 Level 49mSec sequence of of anneal, Group type FIG. 2 FIG. 2 peak temp NBTIGroup I msec none none 1200 C. Reference cell (ref) Group II msec +nanosec (i) msec + 800 C. 1300 C. same as ref. nanosec I (ii) msec + 900C. 1200 C. same as ref. nanosec II Group III msec + 900 C. 1300 C. 1200C. same as ref. nanosec + msec Group IV msec + 900 C. multiple 200 mVmultiple (10) nano- improvement nanosec sec pulses over ref. cell at1300 C.

FIG. 3 shows a reliability graph of NBTI, comparing pFET cells shown inTABLE 1. The x-axis of the graph represents slope of the statisticaldistribution and the y-axis represents gate voltage (V) to induce a 50mV threshold voltage shift. The triangles “□” represent the pFET cellsin Group IV (e.g., pFET cells subjected to multiple (10×) nanosecond(e.g., 20-40 nanoseconds) pulsed laser anneals at a peak temperature of1300° C.) and millisecond preheat of 900 C; whereas the circles “♦”represent pFET cells in Group I (the reference cell), the pluses “+”represent pFET cells in Group II(i), the diamonds “0” represent pFETcells in Group II(ii), the crosses “x” represent pFET cells in GroupIII.

As shown in FIG. 3, the pFET cells in Groups I, II and III are mainlydistributed between 2.10 V and 2.18 V. However and surprising to theinventors, the pFET cells in Group IV are mainly distributed between2.28 V and 2.43 V, which is a significant improvement over the otherpFET cells. Accordingly, FIG. 3 shows the superior improvements attainedby implementing the processes of the present invention. Here, theunexpected results show a demonstration of a marked improvement of theproperties, over the results achieved under other process conditions,such that this cannot be classified simply as one of degree alone. Also,these results are of such significance that they provide a practicaladvantage by significantly increasing NBTI, i.e., superiority in aproperty of the material stack, which was not observed by the knownprocesses.

FIG. 4 shows another reliability graph of NBTI, comparing pFET cellsshown in TABLE 1. The x-axis of the graph represents pFET cellssubjected to different annealing processes; whereas the y-axisrepresents gate voltage (V) to induce a 50 mV threshold voltage shift.In this graph, the grouping of pFET cells is the same as in TABLE 1

Here, again, it is shown that a significant improvement in NBTI isachieved in the pFET cells in Group IV which were subjected to theannealing processes of the present invention. More specifically, asshown in FIG. 4, the NBTI improved by ˜200 mV for pFET cells subjectedto the annealing process of Group IV, which designates a 900° C. mSecpreheat with ten (10×) ˜40 nanosecond exposure time pulses with ˜1300°C. peak temperature; compared to pFET cells subjected to the annealingprocesses of Groups I, II, and III.

Gate dielectric capacitance in inversion was also measured. All cellshad similar statistical distribution of the gate capacitance. The gatecapacitance is typically normalized to the silicon oxide dielectricpermittivity and expressed in Angstroms of the equivalent silicon oxide,Tiny. When normalized in such way and without any quantum-mechanicalcorrections, all cells yielded equivalent thickness in inversion of13+/−0.1 A. Hence, the observed improvement in NBTI shown FIGS. 3 and 4was achieved without increasing Tiny in accordance with aspects of theinvention.

FIG. 5 shows a graph of pFET linear threshold voltage for a large, 10um-wide and 1 um-gate-length transistors, Vtlin, comparing pFET cellsshown in TABLE 1. The x-axis of the graph represents pFET cellssubjected to different annealing processes defined in TABLE 1; whereasthe y-axis represents Vtlin (V). In this graph, it is shown that thereare no significant changes in Vtlin amongst the different cells whilethe Group IV shows a 40 mV increase of the absolute value of the pFETlinear threshold voltage. While the observed shift in threshold voltagewill have a small impact on selecting specific transistor operatingpoints, because it can be adjusted by changing workfunction of the gateelectrode material, it, nevertheless, points to a change in materialcharacteristics of gate dielectric material when subjected to multiple(10×) nanosecond (e.g., ˜40 nanosecond exposures) pulsed laser annealsat a peak temperature of ˜1300° C., in accordance with aspects of theinvention. Specifically, the shift of 40 mV is equivalent to a change indielectric fixed charge or charged trap density of ˜1e−7 Coulomb/cm² or˜7e11 #/cm², respectively. The sign of threshold voltage shiftsindicates either a reduction in negative charge or negatively chargedtraps or an increase in positive charge or positively charged traps.This represents an unusual material behavior in the context ofsignificant improvements in NBTI that is typically associated with thereduction of positively charged traps.

FIG. 6 shows a graph of mobility at 1 MV/cm E-field, comparing the pFETcells shown in TABLE 1. The x-axis of the graph represents pFET cellssubjected to different annealing processes defined in TABLE 1; whereasthe y-axis represents mobility of holes in the FET channels. This graphshows that there is no significant degradation in mobility of amongstthe different cells.

The method(s) as described above is used in the fabrication ofintegrated circuit chips. The resulting integrated circuit chips can bedistributed by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed:
 1. A method of forming a semiconductor structure,comprising: forming a gate stack comprising an interfacial dielectricmaterial on a semiconducting material and a high-k dielectric materialon the interfacial dielectric material; and heating the gate stack to apreheat temperature; heating the gate stack to a millisecond preheattemperature; and exposing the gate stack to multiple nanosecond laserpulses at a peak temperature, wherein the peak temperature is below amelting point of the semiconducting material and above amicro-crystallization threshold temperature of the high-k dielectricmaterial.
 2. The method of claim 1, wherein the exposing the gate stackto the multiple nanosecond laser pulses changes a materialcharacteristic of the high-k dielectric material.
 3. The method of claim1, wherein the multiple nanosecond laser pulses comprises 5-100 pulses.4. The method of claim 3, wherein a single pulse duration of themultiple nanosecond laser pulses comprises 10-100 nanoseconds.
 5. Themethod of claim 1, wherein a cumulative laser exposure time ranges from300 nanoseconds to 3 microseconds.
 6. The method of claim 5, wherein themultiple nanosecond laser pulses are performed post gate dielectricdeposition.
 7. The method of claim 1, wherein the semiconductingmaterial includes III/V or II/VI compound semiconductors.
 8. The methodof claim 1, wherein the semiconducting material comprises group IVsemiconductor materials.
 9. The method of claim 8, wherein thesemiconducting material comprises Si and a peak temperature range isfrom 1200° C. to 1400° C.
 10. The method of claim 1, wherein themultiple nanosecond laser pulses are provided post gate dielectricdeposition.
 11. The method of claim 1, wherein the semiconductingmaterial is n-type semiconductor material.
 12. The method of claim 1,wherein the multiple nanosecond laser pulses comprises 40-50 nsecexposure time for a single pulse process.
 13. The method of claim 1,wherein: the millisecond preheat temperature is less than themicro-crystallization threshold temperature of the high-k dielectricmaterial; the millisecond preheat temperature is greater than thepreheat temperature; and the peak temperature is greater than themillisecond preheat temperature.
 14. The method of claim 1, wherein: themillisecond preheat temperature is greater than the preheat temperature;and the peak temperature is greater than the millisecond preheattemperature.
 15. A method of forming a semiconductor structure,comprising: forming a transistor on a semiconducting material, thetransistor comprising a gate stack composed of high-k dielectricmaterial and gate electrode material; and affecting a negative-biastemperature instability (NBTI) in the semiconductor structure by:heating the gate stack to a preheat temperature; heating the gate stackto a millisecond preheat temperature; and exposing the gate stack tomultiple nanosecond laser pulses at a peak temperature below a meltingpoint of the semiconducting material, wherein a cumulative laserexposure time ranges from 300 nanoseconds to 3 microseconds.
 16. Themethod of claim 15, wherein the multiple nanosecond laser pulsescomprises 5 to 100 pulses.
 17. The method of claim 16, wherein a singlepulse duration of the multiple nanosecond laser pulses comprises 10-100nanoseconds.
 18. The method of claim 15, wherein the gate stack is apFET gate stack composed of the high-k dielectric material.
 19. Themethod of claim 15, wherein the exposing the gate stack to multiplenanosecond laser pulses changes a material characteristic of the high-kdielectric material.
 20. The method of claim 15, wherein: themillisecond preheat temperature is less than a micro-crystallizationthreshold temperature of the high-k dielectric material; the millisecondpreheat temperature is greater than the preheat temperature; and thepeak temperature is greater than the millisecond preheat temperature.